Introduction

A high performance JSON library written in ANSI C.

Features

Fast: can read or write gigabytes per second JSON data on modern CPU.
Portable: compliance with ANSI C (C89).
Standard: strict compliance with RFC 8259 standard.
Safe: complete JSON form, number format and UTF-8 validation.
Accuracy: can read and write int64, uint64 and double numbers accurately.
Less Restriction: support unlimited JSON level, \u0000 and non null-terminated string.
Extendable: options to allow comments, trailing commas, nan/inf, custom memory allocator.
Developer Friendly: only one h and one c file, easy to integrate.

Limitations

An array or object is stored as some data structure like linked list, access elements with index or key is slower than iterator.
Duplicate keys are allowed in an object, and the order of the keys is preserved.
JSON parsing result is immutable, a mutable copy is required for modification.

Performance

Benchmark project and dataset: yyjson_benchmark

The simdjson's new On Demand API is faster if most JSON fields are known at compile-time. This benchmark project only checks the DOM API, a new benchmark will be added later.

AWS EC2 (AMD EPYC 7R32, gcc 9.3)

twitter.json	parse (GB/s)	stringify (GB/s)
yyjson(insitu)	1.80	1.51
yyjson	1.72	1.42
simdjson	1.52	0.61
sajson	1.16
rapidjson(insitu)	0.77
rapidjson(utf8)	0.26	0.39
cjson	0.32	0.17
jansson	0.05	0.11

iPhone (Apple A14, clang 12)

twitter.json	parse (GB/s)	stringify (GB/s)
yyjson(insitu)	3.51	2.41
yyjson	2.39	2.01
simdjson	2.19	0.80
sajson	1.74
rapidjson(insitu)	0.75
rapidjson(utf8)	0.30	0.58
cjson	0.48	0.33
jansson	0.09	0.24

More benchmark reports with interactive charts (update 2020-12-12)

Platform	CPU	Compiler	OS	Report
Intel NUC 8i5	Core i5-8259U	msvc 2019	Windows 10 2004	Charts
Intel NUC 8i5	Core i5-8259U	clang 10.0	Ubuntu 20.04	Charts
Intel NUC 8i5	Core i5-8259U	gcc 9.3	Ubuntu 20.04	Charts
AWS EC2 c5a.large	AMD EPYC 7R32	gcc 9.3	Ubuntu 20.04	Charts
AWS EC2 t4g.medium	Graviton2 (ARM64)	gcc 9.3	Ubuntu 20.04	Charts
Apple iPhone 12 Pro	A14 (ARM64)	clang 12.0	iOS 14	Charts

For better performance, yyjson prefers:

A modern processor with:
- high instruction level parallelism
- excellent branch predictor
- low penalty for misaligned memory access
A modern compiler with good optimizer.

Sample Code

Read JSON string

const char *json = "{\"name\":\"Mash\",\"star\":4,\"hits\":[2,2,1,3]}";

// Read JSON and get root
yyjson_doc *doc = yyjson_read(json, strlen(json), 0);
yyjson_val *root = yyjson_doc_get_root(doc);

// Get root["name"]
yyjson_val *name = yyjson_obj_get(root, "name");
printf("name: %s\n", yyjson_get_str(name));
printf("name length:%d\n", (int)yyjson_get_len(name));

// Get root["star"]
yyjson_val *star = yyjson_obj_get(root, "star");
printf("star: %d\n", (int)yyjson_get_int(star));

// Get root["hits"], iterate over the array
yyjson_val *hits = yyjson_obj_get(root, "hits");
size_t idx, max;
yyjson_val *hit;
yyjson_arr_foreach(hits, idx, max, hit) {
    printf("hit%d: %d\n", (int)idx, (int)yyjson_get_int(hit));
}

// Free the doc
yyjson_doc_free(doc);

// All functions accept NULL input, and return NULL on error.

Write JSON string

// Create a mutable doc
yyjson_mut_doc *doc = yyjson_mut_doc_new(NULL);
yyjson_mut_val *root = yyjson_mut_obj(doc);
yyjson_mut_doc_set_root(doc, root);

// Set root["name"] and root["star"]
yyjson_mut_obj_add_str(doc, root, "name", "Mash");
yyjson_mut_obj_add_int(doc, root, "star", 4);

// Set root["hits"] with an array
int hits_arr[] = {2, 2, 1, 3};
yyjson_mut_val *hits = yyjson_mut_arr_with_sint32(doc, hits_arr, 4);
yyjson_mut_obj_add_val(doc, root, "hits", hits);

// To string, minified
const char *json = yyjson_mut_write(doc, 0, NULL);
if (json) {
    printf("json: %s\n", json); // {"name":"Mash","star":4,"hits":[2,2,1,3]}
    free((void *)json);
}

// Free the doc
yyjson_mut_doc_free(doc);

Read JSON file with options

// Read JSON file, allowing comments and trailing commas
yyjson_read_flag flg = YYJSON_READ_ALLOW_COMMENTS | YYJSON_READ_ALLOW_TRAILING_COMMAS;
yyjson_read_err err;
yyjson_doc *doc = yyjson_read_file("/tmp/config.json", flg, NULL, &err);

// Iterate over the root object
if (doc) {
    yyjson_val *obj = yyjson_doc_get_root(doc);
    yyjson_obj_iter iter;
    yyjson_obj_iter_init(obj, &iter);
    yyjson_val *key, *val;
    while ((key = yyjson_obj_iter_next(&iter))) {
        val = yyjson_obj_iter_get_val(key);
        printf("%s: %s\n", yyjson_get_str(key), yyjson_get_type_desc(val));
    }
} else {
    printf("read error (%u): %s at position: %ld\n", err.code, err.msg, err.pos);
}

// Free the doc
yyjson_doc_free(doc);

Write JSON file with options

// Read the JSON file as a mutable doc
yyjson_doc *idoc = yyjson_read_file("/tmp/config.json", 0, NULL, NULL);
yyjson_mut_doc *doc = yyjson_doc_mut_copy(idoc, NULL);
yyjson_mut_val *obj = yyjson_mut_doc_get_root(doc);

// Remove null values in root object
yyjson_mut_obj_iter iter;
yyjson_mut_obj_iter_init(obj, &iter);
yyjson_mut_val *key, *val;
while ((key = yyjson_mut_obj_iter_next(&iter))) {
    val = yyjson_mut_obj_iter_get_val(key);
    if (yyjson_mut_is_null(val)) {
        yyjson_mut_obj_iter_remove(&iter);
    }
}

// Write the json pretty, escape unicode
yyjson_write_flag flg = YYJSON_WRITE_PRETTY | YYJSON_WRITE_ESCAPE_UNICODE;
yyjson_write_err err;
yyjson_mut_write_file("/tmp/config.json", doc, flg, NULL, &err);
if (err.code) {
    printf("write error (%u): %s\n", err.code, err.msg);
}

// Free the doc
yyjson_doc_free(idoc);
yyjson_mut_doc_free(doc);

Documentation

Home Page

TODO

Add documentation page.
Add GitHub workflow for CI and codecov.
Add more tests: valgrind, sanitizer.
Support JSON Pointer to query value from document.
Add fuzzer.
Add RAW type for JSON reader and writer.
Add streaming API for JSON reader and writer.
Add documentation about performance.
Optimize performance for 32-bit processor.

License

This project is released under the MIT license.

iSLC/yyjson